Sushi in Athens doesn't get any better than this. Tell Antonis Drakoularakos, the Tokyo-trained chef who holds court behind the counter, your budget and he'll prepare a feast of local seafood sliced up as sashimi (raw fish) and nigiri (atop vinegared rice). It's a tiny place so book ahead at least a month to be sure of a spot.
You can also order a la carte (sushi from €3 for two pieces) but it really is best to put your trust in Drakoularakos' choices.